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Query: UMLS:C0519030 (Klebsiella)
 21,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Klebsiella aerogenes NCIB 418 assimilates glycerol via alternative pathways: one involves a glycerol kinase with a high affinity for glycerol (apparent Km = 1-2x10(-6)M), and the second a glycerol dehydrogenase with a much lower affinity for its substrate (apparent Km=2-4x10(-2)M). In variously-limited chemostat cultures, one or the other pathway predominated. Thus, aerobic carbon-limited organisms contained only the glycerol kinase pathway whereas aerobic sulphate-limited or ammonia-limited organisms (grown on glycerol) used only the glycerol dehydrogenase pathway. Anaerobic cultures invariably contained glycerol dehydrogenase, and glycerol kinase was absent. Washed suspensions of aerobically-grown organisms oxidized glycerol with kinetics similar to that of the particular enzyme (the primary enzyme of the assimilatory pathway) which they possessed, thus indicating a close association between these two enzymes and the uptake process. But a supply of exogenous glycerol was not a prerequisite for the synthesis of either glycerol kinase or glycerol dehydrogenase, and nor was molecular oxygen the key factor in effecting modulation between the alternative pathways of glycerol metabolism, as had been previously suggested. The physiological significance of dual pathways of glycerol assimilation is discussed.
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PMID:Dual pathways of glycerol assimilation in Klebsiella aerogenes NCIB418: their regulation and possible functional significance. 115 97

Carbon-limited chemostat cultures of Klebsiella aerogenes NCTC 418 consumed more oxygen per unit of cell synthesis when growing on mannitol or glycerol than when growing on glucose; and since the "maintenance" requirements were similar, this suggested that the extra reducing equivalents present in these compounds were oxidized wastefully. By comparison with carbon-limited cultures, carbon-sufficient cultures that were ammonia-, sulphate- or phosphate-limited generally consumed considerably more oxygen per unit of cell synthesis, particularly at low growth rates. Thus, according to the theory of Pirt, these carbon-sufficient cultures had a greatly increased "maintenance energy" requirement but nevertheless used the remaining energy with a much increased efficiency compared with carbon-limited cultures. This, we suggest, is a false conclusion which stems from the basic assumption that the maintenance requirement does not change with growth rate.
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PMID:Bioenergetic aspects of aerobic growth of Klebsiella aerogenes NCTC 418 in carbon-limited and carbon-sufficient chemostat culture. 125 19

The expression under microaerobic conditions of the Rhizobium meliloti nifA and consequently the nifHDK genes was found to be negatively regulated by ammonia and nitrate. Assimilation of the ammonia to glutamate and glutamine is not required for this regulation to occur. This indicates that ammonia itself, and not a product of its metabolism, may be regulating nif expression. Unlike the situation in Klebsiella pneumoniae, NtrC is apparently not involved in mediating the ammonia effect on nifA expression in R. meliloti. Neither does the fixK gene product, which is known to regulate nifA in R. meliloti, appear to be involved in mediating the ammonia effect. The regulation of nifA by ammonia is shown to be mediated through the FixL protein. A truncated fixJ gene, the product of which has been shown to induce nifA expression irrespective of the oxygen status of the cell, also circumvented the repressive effect of ammonia on nifA expression. This suggests that the ammonia effect is mediated through the FixLJ regulatory cascade. Interestingly no effect of ammonia on fixK expression was observed.
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PMID:Ammonia regulation of the Rhizobium meliloti nitrogenase structural and regulatory genes under free-living conditions: involvement of the fixL gene product? 140 87

Citrate is fermented by Klebsiella pneumoniae to 2 acetate, 0.5 formate and 1.2 CO2. The formation of less than 1 formate and greater than 1 CO2 per citrate can be accounted for by the oxidation of formate to CO2 in order to provide reducing equivalents for the assimilation of citrate into cell carbon. A membrane-bound electron transport chain is apparently involved in NADH synthesis by these cells. The electrons from formate oxidation to CO2 are used to reduce ubiquinone to ubiquinol by membrane-bound formate dehydrogenase and ubiquinol further delivers its electrons to NAD+, if this endergonic reaction is powered by delta mu Na+. The endogenous NADH level of K. pneumoniae cells thus increased in the presence of formate in response to a delta pNa+ greater than -100 mV. NADH formation was completely abolished in the presence of oxygen or after addition of hydroxyquinoline-N-oxide, a specific inhibitor of the Na(+)-translocating NADH:ubiquinone oxidoreductase. The increase of endogenous NADH was dependent on the delta pNa+ applied to the cells. Inverted membrane vesicles of K. pneumoniae catalysed the reduction of NAD+ to NADH with formate as electron donor after application of delta mu Na+ of about 120 mV consisting of delta pNa+ of 60 mV and delta psi of the same magnitude. Neither the delta pNa+ nor the delta psi of this size alone was sufficient to drive the endergonic reaction. Strictly anaerobic conditions were required for NADH formation and hydroxyquinoline-N-oxide completely inactivated the reaction.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:NADH formation by Na(+)-coupled reversed electron transfer in Klebsiella pneumoniae. 150 43

A gene bank of Azospirillum lipoferum Br17 constructed in the vector lambda GEM11 was screened with a Bradyrhizobium japonicum nifA gene probe. A 7.3 kb EcoRI fragment carrying a nifA-like gene was thereby isolated and subsequently used to screen a gene bank of Azospirillum brasilense Sp7 constructed in pUC18. Two EcoRI fragments of 5.6 kb and 3.6 kb covering the nifA-homology region were found. Mutants with Nif- phenotype were obtained by site-directed Tn5 mutagenesis of the 5.6 kb fragment and subsequent recombination into the A. brasilense Sp7 genome. The mutations were clustered into two loci located at each extremity of the fragment. One of these loci corresponded to nifA and the other to nifB. The nucleotide sequence of nifA of A. brasilense Sp7 was determined. Comparison of the deduced amino acid sequences of NifA of A. brasilense Sp7 and NifA of B. japonicum, Rhizobium leguminosarum biovar trifolii and Klebsiella pneumoniae confirmed that it was a nifA-like gene. Construction of a nifA-lacZ fusion and mapping of the RNA transcriptional start site showed that the nifA-like gene was expressed from an unidentified promoter, under conditions of nitrogen fixation and in the presence of oxygen and ammonia.
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PMID:Identification of a nifA-like regulatory gene of Azospirillum brasilense Sp7 expressed under conditions of nitrogen fixation and in the presence of air and ammonia. 177 63

The steady-state kinetics of reductant-independent ATP hydrolysis by Klebsiella pneumoniae nitrogenase at 23 degrees C at pH 7.4 were determined as a function of component protein ratio (optimal at an oxidized Fe protein/MoFe protein ratio of 3:1) and MgATP concentration (Km 400 microM). Competitive inhibition was observed for MgADP (Ki 145 microM), [beta gamma-methylene]ATP (Mgp[CH2]ppA) (Ki 115 microM), [beta gamma-monofluoromethylene]ATP (Mgp[CHF]ppA) (Ki 53 microM) and [beta gamma-difluoromethylene]ATP (Mgp[CF2]ppA) (Ki 160 microM). The tighter binding of MgADP to free oxidized Fe protein (KD less than 10 microM) than to the oxidized Fe protein-MoFe protein complex (Ki 145 microM) is proposed as the driving force that induces rate-limiting protein dissociation in the catalytic cycle of nitrogenase. The reversible nature of the reductant-independent MgATP-cleavage reaction was demonstrated by an MgADP-induced enhancement of the rate of the phosphate/water oxygen exchange reaction with 18O-labelled phosphate ion. This enhancement, like the reductant-independent ATPase reaction, only occurred with the complex formed by oxidized Fe protein and MoFe protein and not with the individual proteins. The results are discussed in terms of the mechanism of ATP hydrolysis by nitrogenase and other systems involving protein-protein interactions.
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PMID:Nitrogenase of Klebsiella pneumoniae. Reversibility of the reductant-independent MgATP-cleavage reaction is shown by MgADP-catalysed phosphate/water oxygen exchange. 187 10

OCP 9-176 is an oxycephem antibiotic that contains a 2-aminothiazolyl, carboxypropyl side chain at C-7 and a pyridinium thiomethyl group at C-3. OCP 9-176 was generally twofold less active than its sulfur-containing analog ME 1228 against Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Providencia stuartii, Proteus vulgaris, and Serratia marcescens. Activity against Enterobacter cloacae and Citrobacter freundii was equivalent. OCP 9-176 was twofold less active than ME-1228 against Pseudomonas aeruginosa and Acinetobacter species. Activity of the two agents was similar against Staphylococcus aureus and Staphylococcus epidermidis. Although OCP 9-176 inhibited E. coli containing TEM-1 and TEM-2, it was less active than ME-1228. Klebsiella organisms with SHV-1 and K-2 beta-lactamases were inhibited, but TEM-3-containing isolates had MICs of 16 micrograms/ml. OCP 9-176 was minimally hydrolyzed by TEM-1, PSE-1, K-1, and P99, and it was a poor inhibitor of P99. Replacement of sulfur with oxygen does not increase the activity of compounds with sulfopyridinium methyl groups at C-3.
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PMID:In vitro activity of an oxycephem OCP 9-176 compared with its sulfur analog and other beta-lactams. 187 72

The sequence Cys184-Ala-Asp-Cys187 in the NifL protein of Klebsiella pneumoniae, for which a role in oxygen sensing and/or metal binding has been proposed, was altered by introducing two mutations, Cys184----Ala and Cys187----Ala, using oligodeoxyribonucleotide-directed mutagenesis. Neither mutation abolished ammonium or oxygen control of nif transcription, although some impairment of function was apparent. The two Cys residues are therefore unlikely to have a direct role in oxygen sensing or metal binding, but probably make some contribution to protein folding or stability.
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PMID:Cys184 and Cys187 of NifL protein of Klebsiella pneumoniae are not absolutely required for inhibition of NifA activity. 187 2

Translational fusions of the Escherichia coli lacZ gene to Rhodobacter capsulatus nif genes were constructed in order to determine the regulatory circuit of nif gene expression in R. capsulatus, a free-living photosynthetic diazotroph. The expression of nifH, nifA (copies I and II), and nifR4 was measured in different regulatory mutant strains under different physiological conditions. The expression of nifH and nifR4 (the analog of ntrA in Klebsiella pneumoniae) depends on the NIFR1/R2 system (the analog of the ntr system in K. pneumoniae), on NIFA, and on NIFR4. The expression of both copies of nifA is regulated by the NIFR1/R2 system and is modulated by the N source of the medium under anaerobic photosynthetic growth conditions. In the presence of ammonia or oxygen, moderate expression of nifA was detectable, whereas nifH and nifR4 were not expressed under these conditions. The implications for the regulatory circuit of nif gene expression in R. capsulatus are discussed and compared with the situation in K. pneumoniae, another free-living diazotroph.
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PMID:Expression of regulatory nif genes in Rhodobacter capsulatus. 190 15

A pyruvate oxidoreductase with the capacity to support pyruvate-dependent nitrogenase activity in vitro has been purified from the photosynthetic bacterium Rhodospirillum rubrum. The enzyme requires CoA for activity and is irreversibly inactivated by oxygen. The molecular properties and Km values for the substrates have been studied. In supporting nitrogenase activity addition of ferredoxin is required. Overall the enzyme is similar to the nif-specific pyruvate: flavodoxin oxidoreductase purified from Klebsiella pneumoniae.
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PMID:Purification and partial characterization of a pyruvate oxidoreductase from the photosynthetic bacterium Rhodospirillum rubrum grown under nitrogen-fixing conditions. 193 Jan 34


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